Abstract
The oxygen reduction reaction (ORR) is still the most research-intensive aspect of a fuel cell. The sluggish kinetics of the electrocatalysts toward the ORR requires large amounts of platinum to be used as cathode material, which calls for alternatives to replace or minimize the amount of the noble metals used. This study describes the synthesis and complete characterization of a copper metallopolymer (Cu MP) based on a conducting polymer (CP) and single-site catalytic centers for the electrocatalytic ORR. The copper (II) catalyst, embedded in a redox-active and conducting polymeric environment, was pursued as a potential candidate to replace noble metals in fuel cell applications. Performance studies at a rotating disk electrode (RDE) showed that the metallopolymer exhibited a direct four-electron reduction at potentials between −150 and −350 mV vs. the reversible hydrogen electrode (RHE) and high kinetic current densities of over 22.62 mA/cm2. The kinetic current densities obtained at the Cu MP electrode outperformed most of the reported state-of-the art electrocatalysts toward the ORR. Further analysis of the Cu/CP hybrid revealed the copper being largely reduced to the oxidation state +I.
Highlights
IntroductionThe growing energy demand and consumption worldwide still rely on fossil-based fuels
The growing energy demand and consumption worldwide still rely on fossil-based fuels.the depletive reserves in natural resources and the man-made greenhouse effect are calling for clean and sustainable energy conversion/storage technologies, for example, batteries [1,2,3], supercapacitors [4,5,6,7], solar power [8,9], and fuel cells [10,11]
For the synthesis of the polymer, the authors followed a simple one-pot synthesis procedure presented by Jenekhe et al, using 1,4-hydroquinone 2-carboxaldehyde and thiophene as reagents [50]
Summary
The growing energy demand and consumption worldwide still rely on fossil-based fuels. The oxido-pincer-type [56,57] polymer–metal hybrid turned out to show high catalytic activity toward the oxygen reduction reaction with high kinetic current densities, which the authors believe to be a potential candidate to replace the current, expensive Pt-based catalysts. Their ease of synthesis and structural modification makes them attractive to tailor hybrid organicinorganic materials for electrocatalysis. Kingsborough and Swager introduced a salen-3,4ethylenoxythiophene copolymer containing Co 2+/3+ redox centers for the electrocatalytic ORR as a prime example of such an application, but they reported a sensitivity of the imine functionalities in the salen units to hydrolysis that undermined the high catalytic performance of the cobalt (II/III). Since the metallopolymer precipitated in the stock-solution (10 mL vial) over time, the total mass loading was calculated to be less than 255–306 μg/cm Cu MP
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